Antenna array and simultaneous lobing tracking system



E. GOLDBOHM June 9, 1964 ANTENNA ARRAY AND SIMULTANEOUS LOBING TRACKING SYSTEM 3 Sheets-Sheet 1 Filed Dec. 10, 1959 E. GOLDBOHM June 9, 1964 ANTENNA ARRAY AND SIMULTANEOUS LOBING TRACKING SYSTEM 3 Sheets-Sheet 2 Filed Dec. 10, 1959 June 9, 1964 E. GOLDBOHM ANTENNA ARRAY AND SIMULTANEOUS LOBING TRACKING SYSTEM Filed Dec. 10, 1959 3 Sheets-Sheet 3 1 I (0MP. V

so ADDER I ing purposes.

United States Patent 3,136,993 ANTENNA ARRAY AND SHVIULTANEOUS LOBING TRACKING SYSTEM Erich Goldbohm, 57 Koningin Astrid Blvd., Noordwijk, Netherlands Filed Dec. 10, 1959, Ser. No. 858,621 Claims priority, application Netherlands Dec. 11, 1958 Claims. (Cl. 343-14) This invention relates to a directive antenna array.

It is well-known to those versed in the antenna art that by means of broadside arrays many radiation patterns can be generated dependent on the particular geometric and electric configuration of the individual radiating elements.

Below for reasons of clarity of expression the terms to radiate and to feed will be used for transmitting antennas as well as for receiving antennas. This is admissible because of the reciprocity law, without in any way deducting from the validity of the conclusions drawn.

Especially with centimetre waves so-called slotted wave guides offer many advantages, such slotted wave guides consisting of a wave guide with slots arranged in the walls thereof.

The phase and the amplitude of the wave radiated by these slots are dependent on the location and direction of the slots. With centerfed slotted wave guides two generic cases can be distinguished, i.e. the arrangement in which the radiating elements at both sides of the center are in phase and the arrangement in which the radiating ele ments at both sides of the center are of opposite phase. In the former case a so-called even radiation pattern is generated, which if the array is designed correctly, consists of a single main lobe without minor lobes, whilst in the latter case a so-called odd radiation pattern is generated, giving rise to two symmetrical main lobes, between which a sharp null in the direction at right angles to the array occurs. In the latter case the two main lobes are exactly 180 degrees out of phase with respect to each other. The sharp null makes an antenna which generates an odd radiation pattern very suitable for direction find- If a source of radiation is to be tracked by means of an automatic servo system the difiiculty arises that if the antenna is exactly trained at the source no signal at all is received, whereby the information which is contained in the signal radiated by said source is not available.

It is an object of the invention to provide an antenna array which makes it possible to accurately track a source of radiation and which at the same time provides an output signal due to the radiation received.

In order to obtain this and other desirable results which will be more fully discussed below it is a feature of the antenna array according to the invention when used for reception purposes that the array is designed so as to stimultaneously give rise to an odd pattern (for tracking purposes) as well as an even pattern (as a source of a reference signal and an information-carrying signal). For transmitting purposes the antenna array is so fed, that only an even pattern is generated, because the even pattern concentrates the radiated energy more narrowly.

For that purpose both halves of the slotted wave guide are connected to the equivalent branches of a first magic tee, the E- and H-branch respectively of which are connected to the E- and H-branch respectively of a second magic tee, in the equivalent branches of which the inputs of two identical amplifiers or detectors are arranged, the lengths of the Wave guides interconnecting the E- and H- branches respectively being so chosen that the electrical distances from points in the E- and H-branches respectively of the first magic tee where an incoming planar wave 3,136,993 Patented June 9, 1964 front generates signals of equal phase to any of the inputs in the equivalent branches of the second magic tee differ by a straight multiple of M2, zero included.

Based on the same principle it also is possible to take hearings in spherical co-ordinates. To this end an antenna array which is rotatable about two axes at right angles to each other comprises two slotted wave guides having a fixed position with respect to each other, these slotted wave guides being so suspended that the first and second slotted wave guide respectively are always at right angles to the first and second rotation axis respectively, both halves of the first and second slotted wave guide respectively being connected to opposite branches of a first and second turnstile junction respectively, the central (round) branches of said turnstile junctions being connected to each other, a second and first pair of identical amplifiers or detectors respectively being connected to the remaining opposite branches of said first and second turnstile junction respectively.

These and other features'and advantages of the antenna array according to the invention will be more apparent after a perusal of the following specification, taken in connection with the drawings, wherein FIGURE 1 is an isometric view of an antenna according to the invention,

FIGURE 2 is a diagram of the radiation patterns appertaining to the antenna shown in FIGURE 1, 2

FIGURE 3 is an isometric view of a simplified'embodh ment of a radar set having an antenna according to FIGURE 1,

FIGURE 4 is an isometric view of an antenna for taking bearings in spherical co-ordinates.

FIGURE 5 is a block diagram of a servo system and information deriving means for use with the embodi ments of FIGURES l, 3 or 4, in which a separate ampli-' fier is provided in each channel.

FIGURE 6 is a fragmentary diagram illustrating microwave switches included in the arms of the antenna to limit the electrical length of such arms,

Referring to FIGURE 1 the halves of a slotted wave guide are shown at 1 and 2. These halves are connected to a magic tee having an E-branch 3 and a H-branch 4. These branches are connected to the corresponding branches 5 and 6 respectively of a second magic tee, the equivalent arms 7 and 8 respectively of which contain probes or detector crystals 9 and 10 respectively;

The operation of a device as shown in FIGURE 1 is discussed with reference to the diagram of FIGURE 2, which shows both radiation patterns which can be obtained by means of the slotted radiator 1, 2 of FIGURE 3 1. The field strength has been-plotted along the vertical travelling waves are generated in the slotted wave guide.

If, however, both halves of the slotted wave guide are fed 180 degrees out of phase a double main lobe 12 results, having a sharp null in the direction at right angles to the slotted wave guide. At both sides of said null waves of opposite phase are radiated, which has been symbolized by drawing the left hand half of the odd pattern below the horizontal axis.

The former conditon will ensue if energy is fed to the slotted wave guide through the H-branch 4 and the latter condition will ensue if energy is fed to the slotted detectors are equal. in a subtracting fashion to'the input of a servo system Wave guide through the E -branch #3. If the slotted wave guide is correctly matched to the branches of the magic tee it is further to be observed that theoreticaly the H-.

branch is perfectly isolated from the E-branch. Several practical difficulties make it impossible to attain this ideal, but an isolation of 30 decibels is easily attainable andreproducible. v I a i The possibility of locating and automatically tracking a radiating target by means of an antenna as shown in FIGURE 1 is discussed below with reference to a few examples. It is assumed that both probes or detectors 9 and 10 have substantially equal sensitivities.

If the target is located in a direction 01 no energy will be induced in the H-branch 4, since the target is outside the even beam. In the E-brauch 3 a voltage E is generated, whereby the voltages at the detectors 9 and 10 respectively amount to respectively. After detection the sign of these voltages is no longer significant, so that the output signals of the These output signals are supplied and which rotates the antenna around an axis which is at right angles to the slotted wave guide. In the aboveexample the resulting'input signal for the servo system is zero, so that the servo system is not energized.

- However, if the target is locatedrwithin the even lobe, as indicated at energy will be induced in the H-branch as well as in the E-branch. .The odd pattern generates a voltage E in the E-branch and the even pattern gencrates a voltage E in the H-bra nch. At the direction shown in the drawing these voltages are of equal magnitude, but this is not essential. Equal'magnitudes have been chosen merely for ease of computation. The energy in the E-branch is again divided between the detectors 9 g and 10, giving rise to a voltage at the detector 9 and a voltage at the detector 10.

The energy in the H-branch, which is caused by the i even radiation pattern and which results in a voltage E is also divided between the detectors 9'and 10, however, without giving rise to a phase difference between the voltages generated at these detectors. Therefore theenergy in the H-branch gives rise to voltage Er /i 2 at the detector 9' and an identical voltage at the detector, 10. Therefore the total voltage at the de- 1 age of the detector ltlwill be zero, so that the resulting drive signal for the servo system will differ from zero.

If the servo system is connected in the appropriate sense it Will rotate the antenna so as to decrease the angle This will proceed until the radiating target is situated immediately in front of the antenna, which in the draw ing has been shown as e A targetin the direction is situated exactly in the null of the odd radiation pattern and the maximumof the even radiation pattern. Therefore no energy'is. fed into the E-branch, Whereas a volt i age E is set up in the H-branch.

The energy insthe H-branch is-dividedbetween the detectors 9 and 10, whereby a voltage is set up at each detector. The output voltages of the detectors will therefore be equal, so that the resulting drive signal for the servo system is zero and the servo system does not rotate the antenna any more." 'From the above it appears that if a target is situated in a direction; I which is not at right angles to the antenna, but "which' lies within the even pattern, the target is caught, Where- Y after the antenna is automatically rotated so as to keep the target in'the direction at rightangles to the antenna.

That this also applies for targets which are situated at the other side of the null appears from the situation indi- V cated byln this caseqalsothe-received energy is divided between the H- and E-branches.

E-branches have equal magnitudes. However, these voltages will include a phase angle of degrees, so

The energy which results from the oddradiation pattern 9 is equallydivided betweentthe detectors 9 and 10 respec-. tively, voltages g, g v 7 i /5 and i i being set up at these detectors respectively. Theenergy in the H-branch, which results from the even radiation pattern, is also equally divided between the detectors 9 and 10Vrespectively, giving rise to a voltage V g at each of these detectors.

Therefore the total voltage across the detector 9 will be 5- i-li'l whereas the total voltage across the detector 10 will amount to 7 Since E E the voltage across the detector 9 will be Zero, whereas the voltage across the detector 10 'will be E T herefore the output. voltage of the'detector 9 will be zero, whereas the output voltage. of'the detector.

10 will differ 'fr'om zero.v This again results in an input signal to the servo system which difiers from zero, hows ever, with opposite polarity as thesignal generated at (p so -that in this case toothe target is tracked, auto- 'matically. s L

So far no particulars have been given about the type of the received signal. This can be either. a continuous Wave, a pulsed wave, a phase modulated wave, a fre- V quency modulated wave or an amplitude modulated wave.

Also the target to'be' tracked need not necessarily. be an active target. It is possible to track passive targets, pro vided that these be'illurninated by wave energy, the track- 'ing being made possible by that part of the illuminating energy which is reflected by the target. e

. Therefore an antenna. based on the principle descfibed V t a j been chosen such that the voltages set up in the H- and. V

above makes it possible to track a moving or stationary target from a moving or stationary location. In contradistinction to known direction finder antennas, which reduce the received signal to zero in the bearing direction the possibility of communication is maintained by an antenna according to the invention, since in the exact direction of bearing the sensitivity of the even radiation pattern is maximum.

The same detectors 9 and 10 which serve for generating the input signal for the tracking servo system, which of course should be nearly zero while the antenna is tracking correctly, may also be employed for handling the information carrying signal, by adding their output voltages in a separate part of the receiver, thus deriving a signal which is a maximum if the antenna is tracking accurately. From this signal the information can be derived. If for instance the antenna is employed as a receiving antenna of a fire control radar (a transmitting antenna, which is mechanically coupled to the receiving antenna, radiating a beam of high frequency pulses in the direction at right angles to the receiving antenna) the range of the target can be derived from the time delay of the received pulses, the direction in which the target is located being indicated by the direction of the antenna.

By means of an antenna as described it is also possible to set up a point-to-point beam link between two vehicles or vessels, each of which may be moving, which especially in war time can be very important, since it is then often necessary to group vessels to convoys. The antenna described not only improves the safety as regards interception of the transmitted messages, since these can be intercepted only over a very restricted area, but moreover at each of the vehicles or vessels provided with antennas according to the invention continuous information about the location and course of the other vehicle or vessel is available.

If moreover the vehicles or vessels are provided with transponders it is also possible to obtain information about the distance between the vehicles or vessels, whereby both of the vessels are continuously informed about the position, course and-speed of the other vessel. By suitably choosing the way of operation of these transponders, employing for instance a pulse code, an automatic identification is also possible. By means of a system as described it is therefore possible to automatically transmit or derive data on the identity, position, course and speed, whilst at the same time a beam communication between the vessels can be maintained. With pulsed signals it is possible to employ one single antenna for transmitting purposes as well as for receiving purposes. An embodiment of such a duplex-antenna is shown in FIGURE 3.

Referring to FIGURE 3, both halves of the slotted wave guide are connected to a magic tee having an E- branch and an H-branch 16. The E-branch 15 via a microwave switch 17, the purpose of which will be explained below, is connected to the E-branch 18 of a second magic tee, the equivalent branches of which contain detectors or probes 19 and 20 respectively. The H- branch 16 of the first magic tee is connected to the H- branch of the second magic tee via means to be explained in detail below.

A magnetron 21 or another source of high frequency pulses is connected to one channel of a short slot hybrid 22,'said channel being terminated by a TR cell 23 at its other extremity. As is well-known to those versed in the art a short slot hybrid comprises two parallel wave guide sections, the small walls of which are adjacent each other and are interrupted over a given distance. The second channel of the short slot hybrid 22 is connected to the H-branch 16 at one extremity and is connected to a TR cell 24 at its other extremity. If the magnetron 21 generates a pulse this pulse will reach the TR cell 23 and ignite it, whereby a total reflection occurs at the TR cell 23. The pulse will pass through the gap in the short slot hybrid 22 and reach the TR cell 24, which will be ignited too, whereby at that extremity as well a total reflection occurs. Therefore all energy leaves the short slot hybrid through the H-branch 16 and is equally divided between both halves 13 and 14 of the slotted wave guide. Since these are excited via the H-branch and consequently are in phase only the even pattern is generated. A small fraction of the energy (approximately -30 decibels) will pass into the E-branch 15, but this fraction is rendered harmless, as will be described below. During reception the energy received by the halves 13 and 14 of the slotted wave guide will be divided between the E- branch and the H-branch. The energy in the E-branch 15 is fed to the detectors 19 and 20 via the microwave switch 17. The energy in the H-branch 16 will divide in the short slot hybrid 22 and will reach the second short slot hybrid 25 via the TR cells 23 and 24, which do not ignite at this low energy level. The channel of the short slot hybrid 25 to which the TR cell 24 is connected is terminated at its other end by a matching impedance 26, which in the embodiment shown is a damping wedge. The channel of the short slot hybrid 25 which is connected to the TR cell 23 is connected to the H-branch of the second magic tee at its other extremity. It can be shown vectorially that all energy from the H-branch 16 ultimately reaches the H-branch 27 of the lower magic tee. Theoretically no received energy at all is absorbed by the magnetron 21 or the matching impedance 26. If the electric difference of path length between the E-branches and H-branches respectively, as measured from points in the E- and H-branches of the upper magic tee where an incoming planar wave front generates signals in phase is substantially equal to a whole multiple of 7\/2, zero included, the same operation as in FIGURE 1 results.

So far the nature of the members 19 and 20 has not been described. In general these members can consist of probes, detectors or heterodyning crystals. 'Usually the input of a radar receiver consists of a heterodyning crystal. For that reasin the device as shown in FIGURE 3 comprises a klystron 28 (or a similar source of heterodyning oscillations), which is coupled to the H-branch of the lower magic tee through a directional coupler 29. The coupling direction of the directional coupler is so chosen that the energy from the klystron 28 is transmitted only in the direction of the heterodyning crystals 19, 20, in which consequently the received signals are subjected to heterodyning with the oscillation generated by the klystron.

Conventional intermediate frequency amplifiers can be connected to the outputs of the heterodyning crystals, but a reasonable phase stability of these amplifiers is desirable. It can be shown that all energy from the magnetron Which might leak through the TR cells 23 and 24 is fed to the matching impedance 26, whereby the crystals 19, 20 are protected from overloading due to leakage energy. If energy which passes into the E-branch 15 due to insuflicient isolation would be permitted to reach the E-branch 18 this energy could possibly damage the crystals 19 and 20 or at least overload them. This can be prevented by connecting an externally controlled microwave switch between the E-branches 15 and 18, such as the microwave switch 17. The microwave switch 17 can be controlled by a modulator circuit 62 which also controls the magnetron 21 in such a way that the microwave switch 17 is closed at least as long as the magnetron 21 is generating high frequency energy.

In the modulator circuit of the magnetron 21 from the triggering pulse a pulse can be derived which closes the microwave switch 17 during the period in which leakage energy could be transmitted through the E-branch 18 to the crystals 19 and 20.

As compared with those tracking radars employing a spinning dipole a radar apparatus according to FIGURE 3 has numerous advantages. First of all the available energy is put to greater use. If a spinning dipole antenna is correctly trained the tracked target is located so that. the target is never situated in the direction of j maximum transmitted energy. This is due to the fact that no pattern which could be compared to the even pattern according to the invention is employed,

Further the system according to the invention provides a continuous flow of information, in contradistinction to systems relying on spinning dipoles or other types of beam switching. Whereas beam switching systems rely on a comparison of two discrete intervals during which the radiated beam is pointed in two extreme directions, the radar apparatus according to FIGURE 3' enables a continuous comparison during the entire reception period. Therefore random fluctuations of the strength of the received signal, such as those caused by aspect variations of the tracked, target, propeller fading and the like, interfere with the. attainable tracking accuracy to a' much smaller extent.

In systems employing beam switching it is usual to employ an amplifier which is switched over in the rhythm of the beam switching action. The system'according to the invention enables a far higher switching rate to be employed with a single amplifier than would be possible signals'or" equal phase and amplitude are set 'up. These signals can be considered as signals'resulting from'the equal phase and magnitude are 'fed to and 34 by the turnstile junction 32, in whichfbranches even pattern of the slotted wave guide 30, 31. Similarly,

the even pattern of the slotted wave guide 36, 37 gener- I ates signals of equal phase and amplitude in the branches 38 and 39. Signals due to the odd pattern of the slotted wave guide 30, 31 are transmitted to the turnstile -junc tion 35 and are there divided between the. detector branches 38 and 39, setting up signals of equal'amplitude but opposite phase;

Consequently the branches 38 and 39 receive signals (of opposite phase) due to the odd patternof the hori zontal slotted wave guide 30,31 and signals (in phase) due to the even pattern of the vertical slotted waveguide 36, 37. Therefore just as in FIGURES 1 and 3 a servo system can be connected toithe outputs'of the detector branches 38 and 39. .If in the detector branches 38 and 39 signals due to the even pattern' of the slotted wave guide 36,37 as well as signals due to'the oddpattern'of the slotted wave guide 3%, 31 are set up, the servo system will rotate'the antenna in a horizontal plane until the with beam switching apparatus, the switching'rate of the switching over the amplifier at a rate which corresponds to the pulse repetition frequency is perfectly feasible, which implies an increase in switching rate by a factor of the order of 50. The more frequent samplingafforded thereby makes for a lower sensitivity to random fluctuations, which greatly enhances the tracking accuracy.- It is also possible to employ two identical amplifier channels, in which case switching over of the amplifiers is superfluous. In the latter case random signal fluctuations have no influence whatsoever on the tracking accuracy.

Besides the slope of the radiation pattern of the odd beam near the null is substantially twice as steep as the width, in the horizontal plane.

signals due to the odd pattern of the horizontal slotted wave guide 30, 31 are reduced tozero. V

QThereby an azimuth. bearing is taken. A special advantage is that the acquisition sector is broader than with the. arrangement of FIGURES 1 and 3, because the even pattermwhich is essential to thefunctioning of the servo system rotating the antenna in the horizontal plane is supplied by thevertical slotted wave guide 36, 37, which has'a. small directivity and-consequently a large beam Since signals due to the odd pattern of "the slotted wave guide'fae, 37 generatesignals (of opposite phase) in the I branches 33, 34 a servo system which rotates the antenna 1 in a vertical plane canjbe connected to'thesebranches. J

The operation of this servo system is analogous to the,

slope of the characteristic of a single beam, as employed in beam switching apparatus, which also increases the tracking accuracy. I

The acquisition sector of the antenna is limited to the width of the even pattern. Ifin special cases this acquisition sector is'insufiicient the even pattern can bebroadened while searching for a target by providing microwave switches in each of the halves of the slotted wave guide. By switching off the outer parts of the slotted broadened too. As soon as a target has been perceived the outer parts of the slotted wave guide are again connected, thus increasing the tracking accuracy.-

operation of the servo system already described and there? fore need not be discussedin detail. V i

For illustrativepurposes' only a receiver for 'use with the embodiments of FIGURES 1, 3 (m4 is shown in FIG- 7 a In FIGURES the s gnal pick-off oraetecibr means a.

shown at 44' and 45' respectively. These components correspond to the components 9, and 10in FIGURE 1,

The embodiments described above enable to take bearings in one co-ordinate direction only. For instance,

if a horizontal slotted wave guide bearings can be taken. For tracking airborne targets hearings in spherical co-ordinates should be taken. This is possible if an antenna as shown in FIGURE'4 is employed. The antenna accordingto FIGURE 4 comprisestwo halves of a slotted wave guide 30, 31 which are connected to opposite is employed azimuth branches of a tumstile junction 32 The two remaining opposite branches 33 and 34 of this turnstile junction containprobes 'or detectors 42,43. The central (round) branch of the turnstile junction 32 is connected to the central branch of a second turnstile junction 35. The branches 36 and'37 of the turnstile junction 35 which. are parallel to the detector branches 33 and 34 are connected to halves of another slotted wave For ease of explanation it is assumed that the slotted Wave guide 30, 31 is arranged horizontally, whereas the slotted wave guide 36, 37 is arranged in a vertical plane.

Signals which reach both branches 30 and 31 with i that position is 'reached the comparator'48 no longer 7 7 gives an output and'the servo system 'is arrested. The 1 servomotor 50, as shown in FIGURES '1 and 3,.rotates,

the components 19and ZOin FIGURE 3 and either 40 and 41 or 42'and 43 in FIGURE 4.- As explained before 'these pick-off means can either be heterodyning crystals or any other convenient means, such as pick-up loops.

The signals generated by the pick-off means 44 and 45 respectively aresupplied to separate amplifiers 46 an d 47- respectively, which can be of any convenient construe tion and which may incorporate heterodyning stages, de

tectors and any other known devices. The amplification factors of the amplifiers 46and 47 respectively should differ as little as is possible, for any gain differences occurring in the channels will be indistinguishable from signal differences at thepick-ofl? means 44 and 45.

The outputs of the amplifiers146and 47 are passed to a comparator circuit 48 whichgives no output if the'signals areequal, thatjis if the source OfIadiatiOnislQcated right in front of the antenna array, but will give an'output if the signals are unequal, that is if the radiation source is located in a different direction. In that case the polarity or, the phase of the comparator output will depend onthe. direction of deviation. of the; radiation source. The output of the comparator is passed to a servo amplifier 49, which delivers its output'to a servo-j; motor 59, which rotates the antenna array/until the radiation source is right in front of the array. Assoon as the antenna around the axis 52.

If the pick-oif means 44 and 45 correspond to the components 40 and 41 respectively in FIGURE 4, the servomotor 50 of FIGURE corresponds to the servomotor 55 in FIGURE 4, which rotates the antenna array around the axis 56. If, however, the pick-off means 44 and 45 correspond to the components 42 and 43 in FIGURE 4, the servomotor 50 of FIGURE 5 corresponds to the servomotor 57 of FIGURE 4, which rotates the antenna array around the axis 58. It will thus be appreciated that an antenna array as shown in FIGURE 4 which can be rotated around two axes, requires two separate servo systems, each constructed as shown in FIGURE 5.

Since it is not easy to maintain the gains of the amplifiers 46 and 47 of FIGURE 5 exactly equal it may be preferable to employ instead a single amplifier that is rapidly switched from one to the other pick-01f means.

If tracking the target is not sufficient, but the information contained in the radiataion from the target should also be made available, this can be effected as indicated in FIGURE 5, by adding the output signals of the amplifiers 46 and 47 respectively in an adding circuit 59, which delivers the combined signal in a lead 60. If two servo systems are employed, as in the embodiment of FIGURE 4, the adding circuit 59 should add the output signals of both pairs of amplifiers 46 and 47 of the servo systems.

The way in which the acquisition sector can be broadened while searching for a target is shown in FIGURE 6. In FIGURE 6 the slotted waveguides 63, 64 and 65, 66 correspond with the waveguide halves 1 and 2 of FIG- URE 1 or the waveguide halves 13 and 14 of FIGURE 3. Microwave switches 67 and 68 respectively are connected between the waveguide sections 63, 64 and 65, 66 respectively. The switches 67 and 68 are simultaneously controlled by a switch unit 69. As long as these microwave switches are in a condition in which they transmit wave energy the entire linear array, consisting of the waveguide sections 63, 64, 65 and 66 is operative and the directivity is maximum. It, however, the switch unit 69 renders the switches 67 and 68 in a condition in which they do not transmit wave energy, the outer waveguide sections 64 and 66 are isolated and the linear array, which then consists of only the sections 63 and 65, exhibits a far smaller directivity. This may be a great asset in searching for a target, since the beam coverage is larger and a target is less easily overlooked. With the embodiment of FIGURE 4 there is no need for artificially broadening the beam while searching for a target, for the even pattern, the width of which is decisive for the possibility of picking up a target, is in this embodiment supplied by a slotted waveguide which has but little directivity in the plane in which the slotted Waveguide supplying the odd pattern has its greatest directivity.

Although in the above description only slotted wave guides have been mentioned other types of linear arrays are suitable as well. Also modifications of the described hybrid types are feasible.

It is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What I claim is:

1. An antenna array, comprising a centerfed linear array, the halves of which are connected to the equivalent branches of a first magic tee, the E- and H-branch respectively of which are connected to the E and H- branch respectively of a second magic tee, in the equivalent branches of which the inputs of two identical signal handling means are arranged, the lengths of the wave guides interconnecting the E- and H-branches respectively of the magic tees being so chosen that the electrical distances are such that signals from an external wave field, traveling along the waveguides interconnecting-the E- and H-branches respectively on arrival at the signal handling means have a phase diiference of a whole multiple of M2, zero included.

2. An antenna array, comprising a centerfed linear array, rotatable about an axis at right angles to the direction along which the linear array extends and the main radiating plane of said array, the halves of which are connected to the equivalent branches of a first magic tee, the E- and H-branch respectively of which are connected to the E- and H-branch respectively of a second magic tee, in the equivalent branches of which the inputs of two identical signal handling means are arranged, the lengths of the wave guides interconnecting the E- and H- branches respectively of the magic tee being so chosen that the electrical distances are such that signals from an external wave field, traveling along the waveguides interconnecting the E- and H-branches respectively, on arrival at the signal handling means have a phase dilference of a whole multiple of M2, zero included, a comparator circuit to which the outputs of said signal handling means are connected, and a servo system that is connected to the comparator circuit and that is adapted for rotating the antenna around said axis.

3. An antenna array, comprising a centerfed linear array, the halves of which are connected to the equivalent branches of a first magic tee, the E- and H-branch respectively of which are connected to the E- and H- branch respectively of a second magic tee, in the equivalent branches of which the inputs of two identical signal handling means are arranged, the lengths of the wave guides interconnecting the E and H-branches respective ly of the magic tees being so chosen that the electrical distances are such that signals from an external wave field, traveling along the waveguides interconnecting the E- and H-branches respectively, on arrival at the signal handling means have a phase difference of a whole multiple of M2, zero included, the wave guide connected to the H-branch of the first magic tee comprising in the order cited: a first channel of a first short slot hybrid, a first TR cell, a first channel of a second short slot hybrid and a matched terminating impedance, the wave guide connected to the H-branch of the second magic tee comprising in the order cited: a second channel of said second short slot hybrid, a second TR cell, a second channel of said first short slot hybrid and a source of high frequency pulses.

4. An antenna array, comprising a centerfed linear array, rotatable about an axis at right angles to the direction along which the linear array extends and the main radiating plane of said array, the halves of which are connected to the equivalent branches of a first magic tee, the

and H-branch respectively of which are connected to the E- and H- branch respectively of a second magic tee, in the equivalent branches of which the inputs of two identical signal handling means are arranged, the lengths of the wave guides interconnecting the E- and H-branches respectively of the magic tees being so chosen that the electrical distances are such that signals from an external wave field, traveling along the waveguides interconnectlng the E- and H-branches respectively, on arrival at the signal handling means have a phase diiference of a whole multiple of M2, zero included, a comparator circuit having inputs to which the outputs of said signal handling means are connected, a servo system that is controlled by the comparator circuit and that is adapted for rotating the antenna around said axis, the wave guide connected to the H-branch of the first magic tee comprising in the order cited: a first channel of a first short slot hybrid, a first TR cell, a first channel of a second short slot hybrid and a matched terminating impedance, the wave guide connected to the H-branch of the second magic tee comprising in the order cited: a second channel of said second short slot hybrid, a second TR cell, a second channel of said first short slot hybrid and a source of high frequency pulses.

I 5. An antenna array, comprising a centerfed linear respectively of which are connected to the E- and H- branch respectively of a second magic tee, in the equivalent branches of which the inputs of two identical signal handling means are arranged, the lengths of the wave guides interconnecting the E- and I-l-branches respective ly of the magic tees being so chosen that the electrical distances are such that signals from an external wave field, traveling along the waveguides interconnecting the 'E; and H-branches respectively, on arrival at thesignal handling means havea phase diiference of a whole multiple of M2, zero included, the wave guide connected to the H-branch of the first magic tee comprising in the order cited: a first channel of a first short slot hybrid, a first TR cell, a first channel of a second short slot hybrid and a matched terminating impedance, the wave guide connected to the H-branch of the second magic tee comprising in the order cited: a'second channel of said second short slot hybrid, a second TR cell, a second' channel of said first short slot hybrid and a source of high frequency pulses, a heterodyning oscillator beingv rection along which the linear array extends and the main radiating plane of'said array, the halves of: which are connected to the equivalentbranches of a first magic tee, the E- and H-branch respectively oflwhich are connected to the E- and H-branch respectively of a second 1% comprising in the order cited: a second channeliof said second short slot hybrid, a second TR cell, a sec ond channel of said first short slot hybrid and a source" of high frequency pulses, a microwave switch being provided in the wave guide joining the E-branches ofboth magic tees, and means synchronizing theclosing rhythm of said microwave switch with the source of high frequency pulses such that said Eebranches are isolated from each other as long as a high frequency pulse is present in the system.

8. An antenna array, comprising a centerfed linear array, rotatable about an axis at right angles to the directionialong which thelinear array extends and the main r '7 radiating plane of said array, the halves of which are connected to'the equivalent'branches of a first'ma gic' tee, the E- and H-branch respectively of which are connected to'the-E- and H-branch respectively of a second magic tee, in the equivalent branches of which the inputs of two identical signal handling'means are arranged,the lengths of thewave guides interconnecting the E- and H- branches respectively of the magic tees being so chosen that the electrical distances are such that signals from an magic tee, in the'equivalent branches, of which the inputs of .two identical signal handling means are arranged, the lengths of the wave guides interconnecting 'the E and H-branchesof the magic tees respectively being so chosen that the electrical distances are such that signals from an external wave field, traveling along the waveguide inter- 7 connecting the E- and H-branches respectively, on' artor circuit having inputs to which the outputs of said signal handling means are connected,sa servo system that is controlled by said circuit and that is adapted 'for rotatingthe antenna around said axis, the wave guide connected to the H-branch of the first magic tee comprising in the order cited: a first channel of a first short slot hybrid, a first TR cell, a first channel of a second short slot hybrid and a matched terminating impedance, the wave guide connected to the H-branch of the second magic tee comprising in the order cited: a second channel of said second short slot hybrid, a second TR cell, a second channel of said first shortlslot hybrid and a source of high frequency pulses, and a heterodyning oscillator that is coupled to one of the branches of the second magic tee through a directional coupler,

7. An antenna array, comprising a centerfed linear array, the halves of which are connected to the equivalent branches of a first magic tee, the Band H-branch re-l spectively of which are connected to the E- and H-branch respectively 'of a second magic tee, in, the equivalent branches of which the inputs of two identical signals handling'means are arranged, the lengths of the wave external wave field, "traveling along the waveguides interconnecting the H- and E-branches respectively, on arrival at the signal handling means have a phase difierence of awhole multiple of M2, zero included, a

comparator circuit having inputs to which the outputs of said signal handling means are connected, a servo system that is controlled by the comparatorrcircuit'and that is adapted for rotating the antenna around"saidaxis, the wave guide connected to the H-branch of the" first magic tee comprising in the order cited: a first chan:

nel of a first short slot hybrid, a first TR' cell, a first channel of a second short slot hybrid and a matched terminating impedancejthe waveguide connected to the H-branch of the second umagic tee comprising in the order cited: -a second channel of saidsecond short slot 7 1 hybrid, asecond TR cell, a second channel of said first short slot hybrid and a source of high frequency pulses,"

a microwave switch being provided in the wave guide joining the 'E-branches of both magic tees, and means synchronizmg-the closing rhythm of said microwave switch with' the source of high frequency pulses such that said -E-branches are isolated from each other as long as a signal handling means have a phase difference of 'a Wl'lO'lQ multiple of M 2, zero included, the wave guide connected to the H-branch of the first magic tee comprising in the order cited: a first channel of a-first short slot hybrid,

a first TR cell, a first channel of a second short slot hybrid and a matched terminating impedance, the wave guide connected to the H-branch of the second magic high frequency pulse is present in the system.

, v9; An antenna'array, 'comprising'a centerfed linear array, the halves of which are connected to the equivalent branches of a first magic tee, the E- and H-branch 'respectively of which are connected to the E- and H-branch respectively of a second magic tee, in the equivalent branches of which the inputs of 'two' identical signal handhng means are arranged, the lengths of the wave guides interconnecting the E-andH-branchesrespectively or the magic tees being so chosen that theelectrical distances are such that the signal from an external wave field," traveling along the'waveguides' interconnecting the H- and E- branches respectively, onarrival at the signal handling means have'a phase difference of a whole mul-' tiple of A/Z, zero included, the wave guidev connected to V the H -branch of the first magic tee comprising in the order cited: a first channel of a first short slot hybrid,,

a first TR cell, a first channel of a second short slot hy-- brid and a matched terminating impedance, the wave" guide connected to the H-branch of the second magic'tee l 7 comprising in the order cited: a second channel of said second short-slot hybrid, a second TR cell, a second channel of said first shortslot hybrid and a source of high frequency pulses, aheterodyning oscillator that is coupied to the one of the branches of thelseeond magic tee through a directional coupler, a microwave switch being provided'in the wave guide joining the E-branches of each other as long as a high frequency pulse is present in the system.

10. An antenna array, comprising a centerfed linear array, rotatable about an axis at right angles to the direction along which the linear array extends and the main radiating plane of said array, the halves of which are connected to the equivalent branches of a first magic tee, the E- and H-branch respectively of which are connected to the E- and H-branch respectively of a second magic tee, in the equivalent branches of which the inputs of two identical signal handling means are arranged, the lengths of the wave guides interconnecting the E- and H-branches respectively of the magic tee being so chosen that the electrical distances are such that signals from an external wave field, traveling along the waveguides interconnecting the H- and E-branches respectively, on arrival at the signal handling means have a phase difference of a whole multiple of M2, zero included, a comparator circuit having inputs to which the outputs of said signal handling means are connected, a servo system that is connected to the comparator circuit and that is adapted for rotating the antenna around said axis, the wave guide connected to the H-branch of the first magic tee comprising in the order cited: a first channel of a first short slot hybrid, a first TR cell, a first channel of a second short slot hybrid and a matched terminating impedance, the wave guide connected to the H-branch of the second magic tee comprising in the order cited: a second channel of said second short slot hybrid, a second TR cell, a second channel of said first short slot hybrid and a source of high frequency pulses, a heterodyning oscillator that is coupled to the one of the branches of the second magic tee through a directional coupler, a microwave switch being provided in the wave guide joining the E-branches of both magic tees, and means synchronizing the closing rhythm of said microwave switch with the source of high frequency pulses such that said E-branches are isolated from each other as long as a high frequency pulse is present in the system.

11. An antenna array which is rotatable about two axes at right angles to each other, comprising two centerfed linear arrays having a fixed position with respect to each other, these linear arrays being so suspended that the first and second linear array are always at right angles to the first and second rotation axis respectively, both halves of the first and second linear array respectively being connected to opposite branches of a first and second turnstile junction respectively, the central (round) branches of said turnstile junctions being connected to each other, a second and first pair of identical signal handling means respectively being connected to the remaining opposite branches of said first and second turnstile junction respectively.

12. An antenna array which is rotatable about two axes at right angles to each other, comprising two centerfed linear arrays having a fixed position with respect to each other, these linear arrays being so suspended that the first and second linear array are always at right angles to the first and second rotation axis respectively, both halves of the first and second linear array respectively being connected to opposite branches of a first and second turnstile junction respectively, the central (round) branches of said turnstile junctions being connected to each other, a second and first pair of identical signal handling means respectively being connected to the remaining opposite branches of said first and second turnstile junction respectively, a first comparator circuit being connected to the outputs of said first pair of signal handling means, the output of said first comparator circuit being connected to the control input of a servo system adapted for rotating the antenna array about said first axis, a second comparator circuit being connected to the outputs of said second pair of signal handling means, the output of said second comparator circuit being connected to the input of a servo system adapted for rotating the antenna array about said second axis.

13. An antenna array comprising at least one centerfed linear array, the halves of which are connected to a pair of signal handling means through two hybrid junctions, in such a way, that signals corresponding to the even pattern of the linear array reach the signal handling means in phase, while signals corresponding to the odd pattern of the linear array reach the signal handling means in counterphase.

14. An antenna array as claimed in claim 1 comprising microwave switches in intermediate parts of each half of the linear array.

15. An antenna array ing microwave switches half of the linear array.

16. An antenna array ing microwave switches half of the linear array.

17. An antenna array ing microwave switches half of the linear array.

18. An antenna array ing microwave switches half of the linear array.

19. An antenna array ing microwave switches half of the linear array.

20. An antenna array ing microwave switches half of the linear array.

21. An antenna array ing microwave switches half of the linear array.

22. An antenna array ing microwave switches half of the linear array.

23. An antenna array as claimed in claim 10 comprising microwave switches in intermediate parts of each half of the linear array.

24. An antenna array as claimed in claim 11 comprising microwave switches in intermediate parts of each half of at least one of the linear arrays.

25. An antenna array as claimed in claim 12 comprising microwave switches in intermediate parts of each half of at least one of the linear arrays.

as claimed in claim 2 comprisin intermediate parts of each as claimed in claim 3 compris in intermediate parts of each as claimed in claim 4 comprisin intermediate parts of each as claimed in claim 5 comprisin intermediate parts of each as claimed in claim 6 comprisin intermediate parts of each as claimed in claim 7 compris in intermediate parts of each as claimed in claim 8 comprisin intermediate parts of each as claimed in claim 9 comprisin intermediate parts of each Worthington Feb. 25, 1958 Kurtz Apr. 25, 1961 

13. AN ANTENNA ARRAY COMPRISING AT LEAST ONE CENTERFED LINEAR ARRAY, THE HALVES OF WHICH ARE CONNECTED TO A PAIR OF SIGNAL HANDLING MEANS THROUGH TWO HYBRID JUNCTIONS, IN SUCH A WAY, THAT SIGNALS CORRESPONDING TO THE EVEN PATTERN OF THE LINEAR ARRAY REACH THE SIGNAL HANDLING MEANS IN PHASE, WHILE SIGNALS CORRESPONDING TO THE ODD PATTERN OF THE LINEAR ARRAY REACH THE SIGNAL HANDLING MEANS IN COUNTERPHASE. 